I'm a member of Ravelry, but don't know too much about it. (yet) How can I find the people who have some yarns for sale? I want to buy some Lion Brand Chenille yarn but don't know how to find someone who's selling it!
Do a search for the yarn:http://www.ravelry.com/yarns/library/lion-brand-lion-chenille-solid/stashes
then you can click on "stashes" to see who has some. If they are willing to sell/trade it they will have it marked.
Look up a specific yarn and you can find who is willing to trade or sell.